Electrode for electron discharge devices



June 7, 1949. H. L. RATCHFORD 2,472,760

ELECTRODE FOR ELECTRON DISCHARGE DEVICES Filed Dec. 30, 1945 /D7'-M/ALLOY JURFACE PLATINUM AND TU/VGS TEN Mme L AA Til/FORD [NV ENTO RATTORN EY Patented June 7, 1949 ELECTRODE FOR. ELECTRON DISCHARGEDEVICES Harry L. Ratchford, Williamsport, Pa., assignor to SylvaniaElectric Products vInc, Emporium, Pa... a corporation of MassachusettsApplication December 30, 1943, Serial No. 516,251

2 Claims.

This invention relates to electron discharge devices andmoreparticularly to the electrodes used in discharge tubes operated athigh temperatures.

One of the difficulties encountered in the operation of thermionic tubesoperated or processed at high temperatures, as power and transmittingtubes, is the occurrence of uncontrolled electron emission from thecontrol grid or any of the other cold discharge electrodes. It is ingeneral desirable that the only source of electron emission be thethermionic cathode (the hot electrode), as primary and secondaryelectron emission from any of the cold tube electrodes influence theelectrical tube characteristics in an undesirable manner.

In tubes designed for operation at high temperatures, the material ofthe grid electrodes must havea high melting point and must have highmechanical strength at high temperatures. These conditions are fulfilledfor certain materials, e. g., tungsten, molybdenum, and tantalum. Thesematerials do, howevenhave the undesirable feature that they have atendency toward secondary and primary electron emission, and collectsome of the emitter material evaporating from the thermionic cathode.Platinum, on the other hand, is very desirable as a material from theviewpoint of low secondary and primary electron emission. Unfortunately,the mechanical strength of platinum is comparatively low, in particularat high temperatures, and what is gained by the use of platinum as agrid material for high temperature operated tubes, considering itsdesirable low electron emission properties is lost again in View of thedeficiency of this material in mechanical stiffness. The characteristicsof tubes incorporating platinum grids vary widely from tube to tube, dueto changes in the shapes of the grids made of this soft material duringthe processing or the life of the tube.

It is, therefore, a principal object of the invention to produceelectron discharge tubes which can be processed and operated at hightemperatures, and whose characteristics do not change from tube to tubeof the same standard design as a result of the softness of their coldelectrodes, and do not exhibit the undesirable effect typical of primaryor secondary electron emission from these electrodes.

One object of the invention relates to means for increasing themechanical stiffness of a grid made of platinum.

According to another object of the invention, means are provided toalloy the surface of a platinum grid structure so as to increase itsmechanical stiffness and to preserve the low electron emissionproperties of platinum.

Another principal object of the invention relates to the use of aplatinum alloy as material for making grids for thermionic tubesoperated at high temperatures, which incorporates the desirable lowelectron-emitting features of platinum combined with a mechanicalstiffness considerably higher than that of platinum.

A feature of the invention relates to means for making grids whichcannot be contaminated by the emitter material evaporating from thethermionic cathode during processing and life of the tube.

In the drawing there is shown in diagrammatic form a grid electrodeembodying the invention.

The invention is based on the fact, that some of the physical propertiesof a metal are usually changed, while others remain constant when a puremetal is alloyed with one or several other metals. Recognizing thesuperior qualities of platinum as a grid material, with respect to itslow electron-emitting properties, but recognizing also the deficiency ofthis material in mechanical stiffness, in particular at hightemperatures, the present invention provides the possibility of alloy-'ing platinum with an appropriate "hardener, resulting in an alloy whichwill preserve the desirable low electron emission properties ofplatinum, but having the desirable increased mechanical stiffness.

According to one embodiment, there is provided an appropriate platinumalloy grid made from a grid made of pure platinum wire. For thispurpose, the ready or preformed platinum grid is sprayed with a lacquersuspension. of fine tungsten powder immediately preceding the mountingof the electrode assembly within the tube. The heat applied to the gridin the ordinary processing of the tube during exhaust running as high as1600 0., results in the formation of a stifier alloy, which howeverstill preserves the low electron-emitting features of platinum. It wasfound that the grid emission of the tubes having platinum grids treatedin this manner was substantially as low as that of tubes made with. pureplatinum grids. At the same time, the stiffness of the grids treated inthis way was found to be considerably higher than that of the grids madeof plain platinum wire, as demonstrated by comparative tests made withgrids of both kinds, namely plain platinum grids and grids treated asdescribed.

According to the above-described embodiment Parts Medium viscosity nitrocellulose (approximately 20 seconds) '1 Diethyl oxalate :10 Butylacetate "30 i Tungsten powder to 10 parts of above lacquer (by weight) 1mounted into a tube, which is then exhausted. During exhaust, thegridlis heated to a'temperature of 1500 to 1600 C.,'for five to tenminutes,

wherebyihedesired alloying of-the tungsten with the'platinum takes:place, "resulting in increased stiffness of the grid'struotureand insubstantial preservation of the low electron-emitting properties of pureplatinum.

It will be understood 'that the invention is not limited'toth'eparticular method of alloying thetungsten andiplatinum described. Thusthe platinum and tungsten rmay 'be alloyed in any well-knowncommercialmanner'and then drawn down to the wire 'size "required for.grid structures. Thus one alloy that was found suitable for the purposeabove described -contained approximately 2-6% tungsten and the balanceplatinum. Preferably, the tungsten should be 4% and the platinum 96%.Instead of using pure "platinum with the tungsten a platinum rhodiumalloy'may be alloyed with the tungsten provided the platinum isthe majorpart of the platinum rhodium portion of the. alloy.

"What is claimed is:

'1. A wire grid electrode 'for use within an electron tube and subjectedto electron bombardment during the normal operation of the tube.

said electrode comprising an alloy of approximately 96% platinum and 4%tungsten to increase the stififness of the electrode while preservingthe low electron-emissive properties of platinum.

2. A gridrelectrode for' use in an=eleotron tube of the type whichemploys a thermionic cathode "I0 i'tending to deposit emissive materialon the grid during .operationoi .the tube, said grid electrode:comprising a platinum base alloy consisting mainly of platinum withfrom 2% to 6% tung- :sten for:inhibiting:primary emission from the gridwhen such emissive material is deposited *thereon and-for the purpose ofincreasing the stifiness of the electrode while preserving the lowemissive properties of platinum.

HARRY L. RATCI-IFORD.

REFERENCES CITED The following referenlces are of "record in 'the fileof this patent:

.UNITED STATES PATENTS Number Name Date 803,684 Fleming Nov. 7, 19051,096,655 Weintraub May1'2, 1914 1,236,383 'Fahrenwal'd Aug.'7,-19171,342,801 Gebauer June 8, 1-920 1,346,192 Gebauer July 13, 1920 407,525Fry =Feb.' 21, 1922 1,566,534 Haagan Dec. '22, 1925 1,655,269 Howe Jan.3, 1928 1,719,774 Metcalf July 2, 1929 2,032,694 Gertler Mar. '3, 19362,183,635 Barker Dec. 19, 1939 2,395,313 {Becker Feb. 19, I946 FOREIGNPATENTS Number Country Date 407,658 GreatiBritain June 14, 1932

